Randy fills in some details about which I've been blissfully
unaware regarding the rubber-bumpered Bs:
> 74 1/2 on MGB's used those dinky, weak, unstable round motor mounts. The
> mounting brackets are different; the front plate *is* different. Sorry, Roger.
Gee, I've never looked under the hood of an RBB. From the sounds of it,
I'm happier that way. :-)
> >> 2) Transmission pilot bushing diameter is smaller on 3 main engines (And
> >> maybe All 3 syncro trannys?)
> >
> >Yes -- all 3-synchro transmissions require a smaller pilot bushing than
> >used on the 4-synchro transmissions (or, well, than used on the ENGINES
> >that came attached to 4-synchro transmissions).
>
> Nope, not quite. The 3 main engine takes a (much) smaller pilot bearing than
> the 5 main. All 4 syncro boxs were behind 5 mains, and therefore have the 1"
> pilot. 3 syncros can be either.
I should have remembered that; I think I worked it out once when I was
thinking about putting a 1.8L into a Magnette. It's been a few years
since I sold the 3-synchro box to Andy and he had to swap out the pilot
bushing from his 5-main engine for the smaller one. (It *can* be done,
though the main motivation here was that I had a race-prepped 3-synchro
box, which is slightly lighter than the 4-synchro box, and Andy needed
a transmission *period* and the lighter one was an added bonus.)
For completeness, here's a chart to make up for my gawping inaccuracy
in the previous posting:
Year Engine Pilot Bushing Gearbox
1962-64 3-main small 3-synchro
1965-67 5-main large 3-synchro
1968-up 5-main large 4-synchro
Of course, the 3-main/3-synchro gearbox is also used in the MGA and the
Magnette, so swapping engines from later Bs into the earlier cars is made
a little more complex than it might at first have appeared. (Is Robert
Neilson still on the list? He had an MGB-motored MGA that was getting
some stuff done to it a year or so ago...)
> >> 3) Engine rear plate may need to be changed when changing between 3 and 3
> >> syncro trannys. ????
> >
> >Yes, I think; the starters are either of different types or in
> >different places. Check the floor pan shape on early vs. late
> >to see what that looks like.
>
> Yes, different starter, and the change was at same time as the change to 4
> syncro. Early style used the infamous inertia bendix with remote solenoid.
> Later style used the solenoid-engaged bendix, hence the solenoid was on the
> starter.
Yes, and for the reference of Mister Daren Stone, you don't put the
brown wires on the bottom peg and the black cable from the battery
on the top peg. :-) Thank goodness the battery was so worn out that
it only made the faintest of sparks when Chris touched the ground
cable to the terminal. All the wires go to one of the posts; the
other post is what gets energized when the solenoid closes as a result
of the white-brown relay wire. (Actually, Chris saw the problem when he
and I were debugging it after Daren and Tim Pettenati had left. The
problem was that while Daren was under the car on the passenger's side,
Tim was standing by the driver's door reading from the diagram, and
in the diagram, the terminal that gets all the wires is on TOP while
on the car, that terminal is on the BOTTOM. Or vice versa, or something.
Anyway, since Tim's off the list for a while I can't give him a hard
time, so I guess Daren is elected.)
On the other hand, Daren, thanks for lending me the trickle charger.
We still didn't get the B running last night, but it should have a
full battery shortly. I'll just leave the car in neutral so I don't
launch it into the washer and dryer... :-)
> How to tell the difference:
> The 3 sycro back plate has the two starter holes inline vertically. Both
> are through-holes. The 4 syncro has the holes canted top out. Bottom hole
> is threaded 3/8-24; the bolt is behind the flywheel and so does not pass
> through into the bellhousing.
Say that again... We haven't tightened down that bottom bolt yet. It's
just a 3/8-24 bolt that goes through the starter and into the backplate,
yes? (It's been a while since we pulled it, I guess...) And the top
bolt on the pre-engaged starter is coarse-threaded and screws into the
aluminum of the bellhousing, right? Something like that... In either
case, it sounds like something I'm going to want to do before I try
to crank the motor to get oil into the galleries (much less drive down
the street).
> The black bumpered cars carry the mounts lower on the engine.
This sounds as though swapping the other way 'round would be more
complex than at first imagined, too. That is, I couldn't just take
my 18GK that I pulled out of The Green Car, rebuild it, and drop it
into a non-rusted '77 MGB to get back some performance without making
the corresponding (but reversed) changes to the mounting pads, right?
Was this done to simplify the V8 conversion, by any chance? It happened
about the same time.
> >> 7) Earlier engines don't have the mounts for alternators.
> >
> >Right, and I'm not sure when the changeover happened. Note also that
> >the wiring harness changed between May 1971
Sorry, my car was built in March '71 (May '71 is when John Thornley retired. :-)
> MGB's got alternators in 71; that weird two plug one. In 72 they went to
> the single plug 16ACR unit. That 71 alt you have is unique, you won't get
> another one. Many years ago, Lucas included a late model plug with every
> alternator for the purpose of retrofitting cars like yours. They no longer
> do this. When you need to convert, you'll have to roll your own plug.
Oh, joy. What's the average lifespan of an alternator, anyway? And
what does it take to rebuild one? (Though I suppose tracing the outputs
of the alternator to the various wires wouldn't be all that difficult.)
--Scott "I guess I won't be getting THIS one for $19.95 at Kragen" Fisher
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